Bug 1541122: [try-staging] Specify bouncer-prefix in cron bouncer check as well; r=mtabara

The previous changes only changed the check in the release process. This also
updates the periodic check.

Differential Revision: https://phabricator.services.mozilla.com/D26199

--HG--
extra : moz-landing-system : lando

taskcluster/ci/cron-bouncer-check/kind.yml

@@ -18,6 +18,8 @@ job-defaults:
         docker-image: {in-tree: "update-verify"}
     run:
         sparse-profile: mozharness
+        extra-config:
+            bouncer_prefix: "https://download.mozilla.org/"
     attributes:
         build_platform: linux64
         build_type: opt